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MGH NEURODIAGNOSTIC SKIN BIOPSY SERVICE |
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| About small-fiber neuropathies |
Less is known about small-fiber sensory neuropathies than about other types of neuropathies, mostly because many conventional tests for painful neuropathies can give false “normal” results and fail to provide evidence of damage to small unmyelinated nerves. Skin biopsies have a better track record (sensitivity) for diagnosing these conditions.1 Rapid progress is being made in this field,2 which will hopefully lead to better treatments.3
Some patients with painful small-fiber sensory neuropathies have underlying causes that can be treated. It is important to look for these causes, because treating them may help reverse the nerve damage. In the United States, diabetes mellitus (high blood sugar) is a leading cause of painful neuropathy. Painful diabetic neuropathy can come on in the very earliest stages of diabetes, before any other symptoms of the disease develop and before the diabetes has even been diagnosed.4 So patients with painful neuropathy should be tested for diabetes.
Heavy alcohol drinking can also damage nerves and should be avoided by neuropathy
patients. HIV or AIDS can cause neuropathy, as can some of the drugs used to
treat HIV.5 In parts of the world where the disease is present, leprosy
can cause neuropathy. Some neuropathies are part of familial, or genetic, syndromes
and may be diagnosed by testing.2 Exposure to neurotoxins, including
some chemotherapy drugs and high doses of vitamin B6 (pyridoxine),
can cause painful neuropathy.6,7
Often, no clear cause of painful neuropathy is found because we are still learning
about what causes these conditions. The term idiopathic small-fiber neuropathy
is often used when the cause of the neuropathy is unknown.8 Certain
blood and urine tests may be appropriate in looking for treatable causes of
painful neuropathy. Click on this link for an MGH
form listing recommended diagnostic tests. The form, which can be printed, can
be helpful when discussing with your doctor which tests might be right for you.
This is information is intended as a general overview of—and not a source
of specific medical advice about—painful small-fiber sensory neuropathies.
For most patients, treatment will focus on reducing symptoms and disability, and helping patients take part in everyday activities as much as possible. Patients with weakness or muscle cramps may need treatments targeting those symptoms as well. For many small-fiber neuropathy patients, chronic pain in the feet and legs will be their major problem. There are several types of medications clinically proven to be useful against pain from neuropathy and related conditions. These include tricyclic antidepressants,9,10 anticonvulsants,11 opioid medications,12,13 and local anesthetics applied to the painful area.14 You may wish to discuss treatment options with your physician if pain becomes a problem.
1. Periquet MI, Novak V, Collins MP, Nagaraja HN, Erdem S, Nash SM, Freimer ML, Sahenk Z, Kissel JT, Mendell JR. Painful sensory neuropathy: prospective evaluation using skin biopsy. Neurology 1999;53:1641-1647.
2. Bejaoui K, Wu C, Scheffler MD, Haan G, Ashby P, Wu L, de Jong P, Brown RH, Jr. SPTLC1 is mutated in hereditary sensory neuropathy, type 1. Nat Genet 2001;27:261-262.
3. Arezzo JC. New developments in the diagnosis of diabetic neuropathy. Am J Med 1999;107:9S-16S.
4. Smith AG, Ramachandran P, Tripp S, Singleton JR. Epidermal nerve innervation in impaired glucose tolerance and diabetes-associated neuropathy. Neurology 2001;57:1701-1704.
5. Verma A, Bradley WG. HIV-1-associated neuropathies. CNS Spectrums 2000;5:66-72.
6. Dalton K, Dalton MJ. Characteristics of pyridoxine overdose neuropathy syndrome. Acta Neurol Scand 1987;76:8-11.
7. Bassler KH. Use and abuse of high dosages of vitamin B6. Int J Vitam Nutr Res Suppl 1989;30:120-126.
8. Holland NR, Crawford TO, Hauer P, Cornblath DR, Griffin JW, McArthur JC. Small-fiber sensory neuropathies: clinical course and neuropathology of idiopathic cases. Ann Neurol 1998;44:47-59.
9. Max MB, Lynch SA, Muir J, Shoaf SE, Smoller B, Dubner R. Effects of desipramine, amitriptyline, and fluoxetine on pain in diabetic neuropathy. New Engl J Med 1992;1250-1256.
10. Kieburtz K, Simpson D, Yiannoutsos C, Max MB, Hall CD, Ellis RJ, Marra CM, McKendall R, Singer E, Dal Pan GJ, Clifford DB, Tucker T, Cohen B. A randomized trial of amitriptyline and mexiletine for painful neuropathy in HIV infection. Neurology 1998;51:1682-1688.
11. Tremont-Lukats IW, Megeff C, Backonja MM. Anticonvulsants for neuropathic pain syndromes: mechanisms of action and place in therapy. Drugs 2000;60:1029-1052.
12. Harati Y, Gooch C, Swenson M, Edelman S, Greene D, Raskin P, Donofrio P, Cornblath D, Sachdeo R, Siu CO, Kamin M. Double-blind randomized trial of tramadol for the treatment of the pain of diabetic neuropathy. Neurology 1998;50:1842-1846.
13. Sindrup SH, Andersen G, Madsen C, Smith T, Brosen K, Jensen TS. Tramadol relieves pain and allodynia in polyneuropathy: a randomised, double-blind, controlled trial. Pain 1999;83:85-90.
14. Kissin I, McDanal J, Xavier AV. Topical lidocaine for relief of superficial pain in postherpetic neuralgia. Neurology 1989;39:1132-1133.
